1. Field of the Invention
The present invention relates generally to solid free form fabrication of objects and, more specifically, to a method of solid free form fabrication of an object.
2. Description of the Related Art
It is known to free-form three-dimensional objects by sequential deposition of molten droplets, falling towards a substrate. Such known examples are disclosed in U.S Pat. Nos.: 5,787,965; 5,807,437; and 5,837,960. During the free-form fabrication process, the molten droplets are formed and projected downward on a substrate to produce a free-form three-dimensional object or rapid tool. When such molten droplets impinge on the substrate, the force of gravity acting on the droplets prior to final solidification of the molten material produces spreading of the droplet, while surface tension acts to contain the liquid volume. This results in an irregularity on an outer surface of the object, which requires finishing of some kind prior to use.
The droplet's velocity also impacts the degree of spreading which occurs, as does the relative amounts of liquid and solid material present in the molten droplet. If the molten droplet is relatively cold, the deposit which forms will have discrete droplets whose outer surface is relatively easily predicted and controlled, however, the interdroplet spaces will be porous, due to the non-fluid nature of the molten droplet. On the other hand, if the molten droplets are highly fluid, they will splat outward, creating a surface, which has inaccurate dimensional control, although porosity will be minimized.
Although the above process has worked well, it desirable to produce a solid free form sprayed object with a smoother and more dimensionally controlled surface. It is also desirable to produce better deposits of the molten droplets when spraying a free-formed object. It is a further object of the present invention to free form an object and eliminate secondary finishing operations.